1. Field of the Invention
The present invention relates generally to neurological disease and, more particularly, to intracranial stimulation for optimal control of movement disorders and other neurological disease.
2. Related Art
There are a wide variety of treatment modalities for neurological disease including movement disorders such as Parkinson""s Disease, Huntington""s Disease, and Restless Leg Syndrome, as well as psychiatric disease including depression, bipolar disorder and borderline personality disorders. These treatment modalities are moderately efficacious; however, they suffer from several severe drawbacks. Each of these traditional treatment modalities and their associated limitations are described below.
One common conventional technique for controlling neurological disease includes the use of dopaminergic agonists or anticholinergic agents. Medical management using these techniques requires considerable iteration in dosing adjustments before an xe2x80x9coptimalxe2x80x9d balance between efficacy and side effect minimization is achieved. Variation, including both circadian and postprandial variations, causes wide fluctuation in symptomatology. This commonly results in alternation between xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d periods during which the patient possesses and loses motor functionality, respectively.
Another traditional approach for controlling movement disorders is tissue ablation. Tissue ablation is most commonly accomplished through stereotactic neurosurgical procedures, including pallidotomy, thalamotomy, subthalamotomy, and other lesioning procedures. These procedures have been found to be moderately efficacious. However, in addition to posing risks that are inherent to neurosurgical operations, these procedures suffer from a number of fundamental limitations. One such limitation is that tissue removal or destruction is irreversible. As a result, excessive or inadvertent removal of tissue cannot be remedied.
Furthermore, undesirable side effects, including compromise of vision and motor or sensory functions, are likely to be permanent conditions. In particular, bilateral interventions place the patient at considerable risk for developing permanent neurologic side effects, including incontinence, aphasia, and grave psychic disorders. An additional drawback to this approach is that the xe2x80x9cmagnitudexe2x80x9d of treatment is constant. That is, it is not possible to vary treatment intensity over time, as may be required to match circadian, postprandial, and other fluctuations in symptomatology and consequent therapeutic needs. Thus, decrease in treatment xe2x80x9cmagnitudexe2x80x9d is not possible while an increase in treatment xe2x80x9cmagnitudexe2x80x9d necessitates reoperation. Some adjustment is possible through augmentation with pharmacologic treatment; however, these additional treatments are subject to the above-noted limitations related to drug therapy.
Another traditional approach for controlling movement disorders and other neurological disease includes tissue transplantation, typically from animal or human mesencephalic cells. Although tissue transplantation in humans has been performed for many years, it remains experimental and is limited by ethical concerns when performed using a human source. Furthermore, graft survival, as well as subsequent functional connection with intracranial nuclei, are problematic. The yield, or percentage of surviving cells, is relatively small and is not always predictable, posing difficulties with respect to the control of treatment xe2x80x9cmagnitude.xe2x80x9d
Another traditional approach for controlling neurological disease is the continuous electrical stimulation of a predetermined neurological region. Chronic high frequency intracranial electrical stimulation is typically used to inhibit cellular activity in an attempt to functionally replicate the effect of tissue ablation, such as pallidotomy and thalamotomy. Acute electrical stimulation and electrical recording and impedance measuring of neural tissue have been used for several decades in the identification of brain structures for both research purposes as well as for target localization during neurosurgical operations for a variety of neurological diseases. During intraoperative electrical stimulation, reduction in tremor has been achieved using frequencies typically on the order of 75 to 330 Hz. Based on these findings, chronically implanted constant-amplitude electrical stimulators have been implanted in such sites as the thalamus, subthalamic nucleus and globus pallidus.
Chronic constant-amplitude stimulation has been shown to be moderately efficacious. However, it has also been found to be limited by the lack of responsiveness to change in patient system symptomatology and neuromotor function. Following implantation, a protracted phase of parameter adjustment, typically lasting several weeks to months, is endured by the patient while stimulation parameters are interactively adjusted during a series of patient appointments. Once determined, an xe2x80x9cacceptablexe2x80x9d treatment magnitude is maintained as a constant stimulation level. A drawback to this approach is that the system is not responsive to changes in patient need for treatment. Stimulation is typically augmented with pharmacological treatment to accommodate such changes, causing fluctuation of the net magnitude of treatment with the plasma levels of the pharmacologic agent.
As noted, while the above and other convention treatment modalities offer some benefit to patients with movement disorders, their efficacy is limited. For the above-noted reasons, with such treatment modalities it is difficult and often impossible to arrive at an optimal treatment xe2x80x9cmagnitude,xe2x80x9d that is, an optimal dose or intensity of treatment. Furthermore, patients are subjected to periods of overtreatment and undertreatment due to variations in disease state. Such disease state variations include, for example, circadian fluctuations, postprandial (after meal) and nutrition variations, transients accompanying variations in plasma concentrations of pharmacological agents, chronic progression of disease, and others.
Moreover, a particularly significant drawback to the above and other traditional treatment modalities is that they suffer from inconsistencies in treatment magnitude. For example, with respect to drug therapy, a decrease in responsiveness to pharmacologic agents eventually progresses to eventually preclude effective pharmacologic treatment. With respect to tissue ablation, progression of disease often necessitates reoperation to extend pallidotomy and thalamotomy lesion dimensions. Regarding tissue transplantation, imbalances between cell transplant formation rates and cell death rates cause unanticipated fluctuations in treatment magnitude. For continuous electrical stimulation, changes in electrode position, electrode impedance, as well as patient responsiveness to stimulation and augmentative pharmacologic agents, cause a change in response to a constant magnitude of therapy.
Currently, magnets commonly serve as input devices used by patients with implantable stimulators, including deep brain stimulators, pacemakers, and spinal cord stimulators. Current systems require the patient to manually turn the system off at night time to conserve battery power and use such magnets to maintain system power. This presents considerable difficulty to many patients whose tremor significantly impairs arm function, as they are unable to hold a magnet in a stable manner over the implanted electronics module. Consequently, many patients are unable to turn their stimulators on in the morning without assistance.
What is needed, therefore, is an apparatus and method for treatment of patients with neurological disease in general and movement disorders in particular that is capable of determining and providing an optimal dose or intensity of treatment. Furthermore, the apparatus and method should be responsive to unpredictable changes in symptomatology and minimize alternations between states of overtreatment and undertreatment. The system should also be capable of anticipating future changes in symptomatology and neuromotor functionality, and being responsive to such changes when the occur.
The present invention is a neurological control system for modulating activity of any component or structure comprising the entirety or portion of the nervous system, or any structure interfaced thereto, generally referred to herein as a xe2x80x9cnervous system component.xe2x80x9d The neurological control system generates neural modulation signals delivered to a nervous system component through one or more intracranial (IC) stimulating electrodes in accordance with treatment parameters. Such treatment parameters may be derived from a neural response to previously delivered neural modulation signals sensed by one or more sensors, each configured to sense a particular characteristic indicative of a neurological or psychiatric condition. Neural modulation signals include any control signal which enhances or inhibits cell activity. Significantly the neurological control system considers neural response, in the form of the sensory feedback, as an indication of neurological disease state and/or responsiveness to therapy, in the determination of treatment parameters.
In one aspect of the invention, a neural modulation system for use in treating disease which provides stimulus intensity which may be varied is disclosed. The stimulation may be at least one of activating, inhibitory, and a combination of activating and inhibitory and the disease is at least one of neurologic and psychiatric. For example, the neurologic disease may include Parkinson""s disease, Huntington""s disease, Parkinsonism, rigidity, hemiballism, choreoathetosis, dystonia, akinesia, bradykinesia, hyperkinesia, other movement disorder, epilepsy, or the seizure disorder. The psychiatric disease may include, for example, depression, bipolar disorder, other affective disorder, anxiety, phobia, schizophrenia, multiple personality disorder. The psychiatric disorder may also include substance abuse, attention deficit hyperactivity disorder, impaired control of aggression, or impaired control of sexual behavior.
In another aspect of the invention, a neurological control system is disclosed. The neurological control system modulates the activity of at least one nervous system component, and includes at least one intracranial stimulating electrode, each constructed and arranged to deliver a neural modulation signal to at least one nervous system component; at least one sensor, each constructed and arranged to sense at least one parameter, including but not limited to physiologic values and neural signals, which is indicative of at least one of disease state, magnitude of symptoms, and response to therapy; and a stimulating and recording unit constructed and arranged to generate said neural modulation signal based upon a neural response sensed by said at least one sensor in response to a previously delivered neural modulation signal.
In another aspect of the invention, an apparatus for modulating the activity of at least one nervous system component is disclosed. The apparatus includes means for delivering neural modulation signal to said nervous system component; and means for sensing neural response to said neural modulation signal. In one embodiment, the delivery means comprises means for generating said neural modulation signal, said generating means includes signal conditioning means for conditioning sensed neural response signals, said conditioning including but not limited to at least one of amplification, lowpass filtering, highpass filtering, bandpass filtering, notch filtering, root-mean square calculation, envelope determination, and rectification; signal processing means for processing said conditioned sensed neural response signals to determine neural system states, including but not limited to a single or plurality of physiologic states and a single or plurality of disease states; and controller means for adjusting neural modulation signal in response to sensed neural response to signal.
Advantageously, aspects of the neurological control system are capable of incorporating quantitative and qualitative measures of patient symptomatology and neuromotor circuitry function in the regulation of treatment magnitude.
Another advantage of certain aspects of the present invention is that it performs automated determination of the optimum magnitude of treatment. By sensing and quantifying the magnitude and frequency of tremor activity in the patient, a quantitative representation of the level or xe2x80x9cstatexe2x80x9d of the disease is determined. The disease state is monitored as treatment parameters are automatically varied, and the local or absolute minimum in disease state is achieved as the optimal set of stimulation parameters is converged upon. The disease state may be represented as a single value or a vector or matrix of values; in the latter two cases, a multi variable optimization algorithm is employed with appropriate weighting factors. Automated optimization of treatment parameters expedites achievement of satisfactory treatment of the patient, reducing the time and number of interactions, typically in physician visits, endured by the patient. This optimization includes selection of electrode polarities, electrode configurations stimulating parameter waveforms, temporal profile of stimulation magnitude, stimulation duty cycles, baseline stimulation magnitude, intermittent stimulation magnitude and timing, and other stimulation parameters.
Another advantage of certain aspects of the present invention is its provision of signal processed sensory feedback signals to clinicians to augment their manual selection of optimum treatment magnitude and pattern. Sensory feedback signals provided to the clinician via a clinician-patient interface include but are not limited to tremor estimates, electromyography (EMG) signals, EEG signals, accelerometer signals, acoustic signals, peripheral nerve signals, cranial nerve signals, cerebral or cerebellar cortical signals, signals from basal ganglia, signals from other brain or spinal cord structures, and other signals.
A further advantage of certain aspects of the present invention is that it provides modulation of treatment magnitude to compensate for predictable fluctuations in symptomatology and cognitive and neuromotor functionality. Such fluctuations include those due to, for example, the circadian cycle, postprandial and nutritional changes in symptomatology, and variations in plasma levels of pharmacologic agents.
A further advantage of certain aspects of the present invention is that it is responsive to patient symptomatology, as tremor typically abates during sleep. This overcomes the above-noted problems of patient inability to hold a magnet in a stable manner over the implanted electronics module and the resulting problem of not being able to turn their stimulators on in the morning without assistance.
A still further advantage of certain aspects of the present invention is that it provides prediction of future symptomatology, cognitive and neuromotor functionality, and treatment magnitude requirements. Such predictions may be based on preset, learned and real-time sensed parameters as well as input from the patient, physician or other person or system.
A still further advantage of certain aspects of the present invention is that it optimizes the efficiency of energy used in the treatment given to the patient. Stimulation intensity may be minimized to provide the level of treatment magnitude necessary to control disease symptoms to a satisfactory level without extending additional energy delivering unnecessary overtreatment.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.